diff --git a/techlibs/xilinx/cells_sim.v b/techlibs/xilinx/cells_sim.v
index fa33f45..1be43f9 100644
--- a/techlibs/xilinx/cells_sim.v
+++ b/techlibs/xilinx/cells_sim.v
@@ -59,6 +59,34 @@
   assign O = I;
 endmodule
 
+module IOBUF (
+    (* iopad_external_pin *)
+    inout IO,
+    output O,
+    input I,
+    input T
+);
+    parameter integer DRIVE = 12;
+    parameter IBUF_LOW_PWR = "TRUE";
+    parameter IOSTANDARD = "DEFAULT";
+    parameter SLEW = "SLOW";
+    assign IO = T ? 1'bz : I;
+    assign O = IO;
+endmodule
+
+module OBUFT (
+    (* iopad_external_pin *)
+    output O,
+    input I,
+    input T
+);
+    parameter CAPACITANCE = "DONT_CARE";
+    parameter integer DRIVE = 12;
+    parameter IOSTANDARD = "DEFAULT";
+    parameter SLEW = "SLOW";
+    assign O = T ? 1'bz : I;
+endmodule
+
 module BUFG(
     (* clkbuf_driver *)
     output O,
diff --git a/techlibs/xilinx/cells_xtra.py b/techlibs/xilinx/cells_xtra.py
index f401ebe..82e403f 100644
--- a/techlibs/xilinx/cells_xtra.py
+++ b/techlibs/xilinx/cells_xtra.py
@@ -326,7 +326,7 @@
     Cell('IBUFGDS', port_attrs={'I': ['iopad_external_pin'], 'IB': ['iopad_external_pin']}),
     Cell('IBUFGDS_DIFF_OUT', port_attrs={'I': ['iopad_external_pin'], 'IB': ['iopad_external_pin']}),
     # I/O.
-    Cell('IOBUF', port_attrs={'IO': ['iopad_external_pin']}),
+    # Cell('IOBUF', port_attrs={'IO': ['iopad_external_pin']}),
     Cell('IOBUF_DCIEN', port_attrs={'IO': ['iopad_external_pin']}),
     Cell('IOBUF_INTERMDISABLE', port_attrs={'IO': ['iopad_external_pin']}),
     Cell('IOBUFE3', port_attrs={'IO': ['iopad_external_pin']}),
@@ -342,7 +342,7 @@
     Cell('OBUFDS', port_attrs={'O': ['iopad_external_pin'], 'OB': ['iopad_external_pin']}),
     Cell('OBUFDS_DPHY', port_attrs={'O': ['iopad_external_pin'], 'OB': ['iopad_external_pin']}),
     # Output + tristate.
-    Cell('OBUFT', port_attrs={'O': ['iopad_external_pin']}),
+    # Cell('OBUFT', port_attrs={'O': ['iopad_external_pin']}),
     Cell('OBUFTDS', port_attrs={'O': ['iopad_external_pin'], 'OB': ['iopad_external_pin']}),
     # Pulls.
     Cell('KEEPER'),
diff --git a/techlibs/xilinx/cells_xtra.v b/techlibs/xilinx/cells_xtra.v
index ce0949f..671d16e 100644
--- a/techlibs/xilinx/cells_xtra.v
+++ b/techlibs/xilinx/cells_xtra.v
@@ -8160,18 +8160,6 @@
     input IB;
 endmodule
 
-module IOBUF (...);
-    parameter integer DRIVE = 12;
-    parameter IBUF_LOW_PWR = "TRUE";
-    parameter IOSTANDARD = "DEFAULT";
-    parameter SLEW = "SLOW";
-    output O;
-    (* iopad_external_pin *)
-    inout IO;
-    input I;
-    input T;
-endmodule
-
 module IOBUF_DCIEN (...);
     parameter integer DRIVE = 12;
     parameter IBUF_LOW_PWR = "TRUE";
@@ -8373,17 +8361,6 @@
     input LPTX_T;
 endmodule
 
-module OBUFT (...);
-    parameter CAPACITANCE = "DONT_CARE";
-    parameter integer DRIVE = 12;
-    parameter IOSTANDARD = "DEFAULT";
-    parameter SLEW = "SLOW";
-    (* iopad_external_pin *)
-    output O;
-    input I;
-    input T;
-endmodule
-
 module OBUFTDS (...);
     parameter CAPACITANCE = "DONT_CARE";
     parameter IOSTANDARD = "DEFAULT";